The present invention relates to a document feeding apparatus for picking documents one by one from a stack of documents, and moving the picked documents away from the stack.
Document feeding apparatus of this kind are commonly of either the vacuum pick or friction pick type. Vacuum pick systems use a suction member to separate the first document from the rest of the stack and are particularly suitable for handling documents which are non-porous, such as currency notes in an automated teller machine (ATM). Friction type pick systems are also used in ATMs and are sometimes advantageous in that they have higher feed rate capabilities than vacuum type pick systems and are of relatively simple construction. Friction pick systems commonly use a rotating pick roller or an endless belt made from a high friction material. When the pick roller or a portion of the belt engages a first document of a stack, the frictional force exerted thereon by the roller or the belt is greater than the frictional force between this document and the next document in the stack, causing the first document to be separated from the stack and moved away by the rotating roller or belt.
In many applications, document feeding apparatus are now required to handle a wide range of media. For example, in addition to currency notes, ATMs now frequently dispense other types of documents such as tickets, travelers cheques, vouchers, sheets of stamps etc. These documents are sometimes in booklet form, where multiple sheets are bound together and are dispensed as a single document by the ATM. A known ATM document feeding apparatus of the friction pick type, which is arranged to handle other types of documents in addition to currency notes, is described in EP0600848. Documents are picked from a stack by a rotating friction roller and are passed into a nip between the friction roller and a pair of rotating stripper rolls, so as to prevent two or more documents from being fed simultaneously. The documents then pass into a gap between the friction roller and a curved guide plate, which serves to guide the documents as they are moved away from the stack by the friction roller towards a further transport system. Basic information relating to the documents to be picked, including whether or not they are currency notes and whether they are new or used, is stored in machine-readable form on the document canister. This information is processed by the ATM controller and the rotational speeds of the pick roller and stripper rolls are adjusted to preset values considered optimum for handling documents of the type identified from the stored information on the document canister.
This known ATM document feeding apparatus is capable of differentiating between four different categories of documents only, i.e., between new currency notes, used currency notes, new non-currency documents and used non-currency documents. However, the characteristics of documents may vary widely within each of these categories, particularly in the case of non-currency documents, where documents may be made from different materials and may have different dimensions. Hence, the preset rotating speeds may not be optimum for all types of documents within a particular category. Moreover, reliable picking of different types of documents by a friction pick mechanism is not solely influenced by the rotating speed of the pick roller or belt, but is dependent on a number of factors. For example, as described earlier, successful friction picking is achieved when the frictional force exerted by the rotating friction roller or belt on the first document of the stack exceeds that existing between the first and adjacent documents of the stack. The frictional forces existing between the documents of the stack is dependent on the frictional properties of the material from which the documents are made and may vary from one type of document to the next. Hence, problems may arise when picking certain types of documents which exhibit relatively high or low coefficients of friction, as the frictional force exerted by the roller or belt on the stack may be insufficient to overcome that between adjacent documents of the stack, or may be of sufficient magnitude to cause the picking of multiple documents simultaneously from the stack.